The present invention relates generally to the field of circuit breakers and more specifically to a circuit breaker having an analog override.
A circuit breaker is typically characterized by a current rating which conventionally corresponds to the current at or above which the circuit breaker will trip (open), disconnecting a source of power from a load. The circuit breaker includes a current transformer (CT) having a winding in close proximity to a power line carrying alternating current. The current transformer provides a sense signal (e.g., a secondary current signal induced by the alternating current of the power line) representative of the power signal in the power line to the control circuitry of the circuit breaker. The control circuitry monitors the secondary current signal and trips the unit based on the monitored signal.
Circuit breakers come in a wide range of current ratings (e.g., 63 Amp, 80 Amp, 160 Amp, 200 Amp, 250 Amp, 400 Amp, 630 Amp, 800 Amp, 1000 Amp, 1250 Amp, 1600 Amp, etc.). Typically, each circuit breaker has a different CT having a rating corresponding to the desired rating of the circuit breaker. The winding of the CT is manufactured to be particularly suitable with the desired rating of the circuit breaker and correspondingly suitable to the current load carried in the power line. With the advent of electronic trip units (ETUs), for monitoring the secondary current signal and for tripping the circuit breaker, it has become necessary to manufacture an ETU for each line of circuit breakers based on the nominal circuit breaker rating.
According to one system, the ETU is provided with a hard-coded program that tells the ETU it is, for example, a 200 Amp circuit breaker. The drawback of this system is that ETUs must be inventoried for each current rating which adds significant cost and complexity to the manufacturing process of the circuit breakers. Another system utilizes programmable ETUs with software tables for all ratings of circuit breakers. A plastic connector (e.g., a jumper) is provided on the circuit board which couples one of a plurality of pins to ground to indicate to the ETU its rating and, correspondingly, which software table to use to interpret (e.g., scale) the secondary current signal. This system requires additional memory space, circuit board space, and added installation steps (e.g., to properly connect the jumper) which adds cost and complexity to the design.
The ETU typically will function, based on its programming, for overcurrent conditions up to eleven times the normal operating current of the system. However, some overcurrent conditions occur in time periods in which the microprocessor in the ETU does not function quickly enough to protect the equipment coupled to the circuit breaker.
There is a need for an analog circuit within the ETU that can respond to an overcurrent condition without relying on the microprocessor in the ETU. Further, there is a need for an improved circuit breaker design that would allow the same microprocessor and software program to be used for current transformers rated from 63 Amps to 1600 Amps, and beyond. Further, there may be circumstances when internal power to the ETU is not available and only external power to the ETU is required to be applied for programming or changing trip-curve parameters. The programming of the ETU is accomplished by a communication protocol imbedded in the ETU firmware and by a connection to a hand-held or table-top computer, that has an identical communication protocol installed and running. The current rating and curve parameters can easily be downloaded to the ETU. The ETU must be powered to be able to communicate. Further still, there is a need for an improved circuit breaker design that would facilitate ease of maintenance, repair, and installation of the circuit breaker.
One embodiment provides a circuit breaker having a trip mechanism and a power line for carrying a power signal from a source to a load and a current transformer configured to sense the power signal and provide a sense signal representative of the power signal to an electronic module in the circuit breaker. The electronic module has a circuit common potential, an application specific integrated circuit (ASIC), a control circuit, a composite circuit which generates a composite signal voltage, and a residual circuit used in ground fault protection. The circuit breaker comprises a first power supply to provide a first voltage signal and a second power supply to provide a second voltage signal. An analog override circuit is configured to receive the first voltage signal from the first power supply, the second voltage signal from the second power supply and the composite signal voltage from the composite circuit. The analog override circuit also provides an override signal to the ASIC. Also included is a logic function configured to receive a first trip signal from the control circuit and a second trip signal from the ASIC and to provide a third trip signal to the trip mechanism. Another embodiment of the circuit breaker includes an external power supply coupled to the electronic module at a point between the first power supply and the second power supply. Such external power supply selectively supplies power only to the second power supply. The second trip signal from the ASIC is provided only when the sum of the first voltage, the second voltage, and the composite voltage signal as determined within the analog override circuit is less than the circuit common potential.
Another embodiment provides an analog override circuit in a circuit breaker. The circuit breaker has a trip mechanism, a power line for carrying a power signal from a source to a load and a current transformer configured to sense the power signal and provide a sense signal representative of the power signal to an electronic module in the circuit breaker. The electronic module has a circuit common potential, an application specific integrated circuit (ASIC), a control circuit, a composite circuit which generates a composite signal, and a residual circuit. The analog override circuit is coupled to the ASIC, a first power supply and a second power supply. The analog override circuit comprises a first resistive circuit configured to receive a first voltage signal from the first power supply and a second resistive circuit configured to receive a second voltage signal from the second power supply and adding the two signals together. A third resistive circuit is configured to receive the composite signal. The sum of the three signals is an override signal that is sent to the ASIC. Another embodiment of the analog override circuit includes a capacitor configured in parallel with at least one resistor in the first resistive circuit. A further embodiment of the analog override circuit includes a logic function configured to receive a first trip signal from the control circuit and a second trip signal from the ASIC and providing a third trip signal to the trip mechanism. The logic function is configured as an OR gate. The analog override circuit can also include an external power supply coupled to the electronic module at a point between the first power supply and the second power supply and selectively providing power only to the second power supply.
A further embodiment provides a circuit breaker having a trip mechanism and a power line for carrying a power signal from a source to a load and a current transformer configured to sense the power signal and provide a sense signal representative of the power signal to an electronic module in the circuit breaker. The electronic module has a circuit common potential, an application specific integrated circuit (ASIC), a control circuit, a composite circuit which generates a composite signal voltage, a residual circuit, comprising a first means for supplying power to provide a first voltage signal and a second means for supplying power to provide a second voltage signal. A means for providing an override signal to the ASIC and a means for receiving a first trip signal from the control circuit and a second trip signal from the ASIC and providing a third trip signal to the trip mechanism.